80 GEORGE LEFEVRE AND WINTERTON C. CURTIS 
have allowed to the work, m certain phases of which, however, 
many others have collaborated. 
The plan of the work has embraced, besides a thorough investi- 
gation of artificial propagation, a detailed study of the life history 
and ecology of the Unionidse, emphasizing especially the geo- 
graphical distribution of the group throughout the Mississippi 
Valley, breeding seasons and habits, physical conditions of the 
waters in which the different species thrive, food enemies, diseases, 
rate of growth, and the behavior of glochidia and fishes, as para- 
sites and hosts, respectively. Although much yet remains to be 
done, results of importance have been obtained, and the entire 
feasibility of artificial propagation clearly demonstrated. 
The writers' personal attention has been largety directed to a 
study of the conditions of reproduction in the group and to the 
parasitism of the larvae from the point of view of their relation to 
artificial infection of fishes with the glochidia, while such phases 
of the investigation as geographical distribution, enemies and 
diseases and general habits have been carried on by others. 
It is through the kindness of the Commissioner of Fisheries, 
the Honorable George M. Bowers, that we have the privilege of 
pubHshing, in advance of our detailed report, certain results 
which bear upon the study of reproduction and parasitism and 
which are briefly presented in this paper. It also gives us pleasure 
to express here our appreciation of the enthusiastic support which 
has been given us by Dr. Barton W. Evermann, Chief of the Divi- 
sion of Scientific Inquiry of the Bureau of Fisheries, whose 
unflagging interest and faith in the investigations since their 
beginning have been largely responsible for such success as has 
been attained. 
As has long been known, the Unionidse carry their young in the 
gills, which function as brood-pouches until the completion of the 
embryonic development. At the close of this period, the larva or 
so-called glochidium is fully formed and escapes from the egg- 
membrane while still within the gill. In some species the dis- 
charge of the glochidia takes place at once, although in others 
